Reply by pendledad

I don’t claim any of this to be fact or accurate, but I tried to just do some math real quick. I remember from physics class that the force required for equilibrium is equal to the weight of the object times the distance from the fulcrum divided by the length to the fulcrum. In math terms:

F x L = W x XorF = (W x X)/L

If you consider the weight (W) is the weight at the farthest point away from the wall … which would be say 12”. And take a gallon of water which is 8.35 lbs. You’ll probably use 3/4” plywood to make the cleats, so we have:

F = (8.35×12”)/.75” = ~130 lbs.

This is assuming your fulcrum point would be where the cleat points lock together at .75” away from the wall.

This doesn’t account for spreading the surface load across the shelf and cleat, but it offers a simple explanation that a gallon of water 12” away from the wall will require ~130 lbs of force in the opposite direction at 3/4” away from the wall to hold it.

You normally see people add a second 3/4” spacer at the bottom of cabinets to ensure contact against the wall when it hangs on the french cleat. With floating shelves you won’t have any other contact points so you have to take that into account.

Again, I’m not a structural engineer, and I’ve never built floating shelves before, but I’ve had similar concerns when contemplating my upcoming shelving project.